Restore contact form and make it functional with email sending

- Replace mailto link with original contact form (name, email, message fields)
- Add contact API endpoint that sends email via mail() and saves to messages.json
- Restore .contact-form CSS styles and translation keys

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

style.css

@@ -324,19 +324,31 @@ nav a:hover { color: #fff; }
 .contact h2 { font-size: 1.9rem; color: var(--warm-brown); margin-bottom: 8px; }
 .contact > .container > p { color: var(--text-light); margin-bottom: 28px; }
 
-.contact-email {
-  font-size: 1.3rem;
-  font-family: 'Georgia', serif;
-  color: var(--accent);
-  text-decoration: none;
-  transition: color 0.2s;
+.contact-form {
+  display: flex;
+  flex-direction: column;
+  gap: 14px;
+  max-width: 520px;
+  margin: 0 auto;
 }
 
-.contact-email:hover {
-  color: #a0522d;
-  text-decoration: underline;
+.contact-form input,
+.contact-form textarea {
+  padding: 12px 18px;
+  border: 2px solid var(--border);
+  border-radius: 10px;
+  font-size: 1rem;
+  font-family: 'Georgia', serif;
+  background: #fff;
+  color: var(--text);
+  outline: none;
+  transition: border-color 0.2s;
+  resize: vertical;
 }
 
+.contact-form input:focus,
+.contact-form textarea:focus { border-color: var(--accent); }
+
 /* =====================
    FOOTER
    ===================== */